A Wellington man's efforts to intervene after hearing his neighbour scream at a group of unwanted visitors to leave her alone were rewarded with a baseball bat smashing to his face.

Police are investigating the incident at a Karori address which took place about 9.15pm last night.The man had heard arguing at his young female neighbour's house, and went to her aid when he heard her screaming for help.

There he witnessed a group of men harrassing the women at her doorstep, who was pleading with them to leave her alone, Detective Grant Nalder said. When the neighbour asked them to leave and they wouldn't, he intervened.

Police were still working to establish exactly what happened next but believe one of the young men - thought to be aged about 19 - struck the neighbour in the face and body several times with a baseball bat, Nalder said. The victim did not require hospital treatment and appeared to have gotten away with cuts and bruises, Nalder said.

The group had arrived at the Karori home with the bat, and police had established that they only knew the woman "second hand," Nalder said.

"A group of people who didn't really seem to know her just came along and they were there to cause trouble. I think they were there to be threatening and possibly to intimidate the female occupant of the house."

Police are speaking to the people involved today and serious assault charges are likely to be laid, Nalder said.